I haven't dealt with probates very much, but with the one i have, the only person appointed by the will or the court which is call executor or executrix has the ability to sign for every body.. trying to get all parties to sign could turn out to be a really hard thing to do.. are you sure everybody needs to sign? my experience is in Pennsylvania, i'm sure Missouri is different..

Wills can be contested, the actions of an administrator or executor(rix) can be contested, partition of rights can be filed and the threat of actions can delay a sale, sometimes for years. Get an acknowledgement from each party to sell or have the court direct the admin/exec to sell. Title folks here would rather see everyone in agreement or court order. :)